The present invention relates generally to antennas loaded by one or more meanderlines (also referred to as variable impedance transmission lines), and specifically to such an antenna providing high gain and frequency tunability through the use of wings affixed to the antenna structure.
It is generally known that antenna performance is dependent upon the antenna shape, the relationship between the antenna physical parameters (e.g., length for a linear antenna, diameter for a loop antenna) and the wavelength of the operating frequency. These relationships determine several antenna parameters, including input impedance, gain, and the radiation pattern shape. Generally, the minimum physical antenna dimension must be on the order of a quarter wavelength of the operating frequency, thereby allowing the antenna to be excited easily and to operate at or near its resonant frequency, which in turn limits the energy dissipated in resistive losses and maximizes the antenna gain.
The burgeoning growth of wireless communications devices and systems has created significant needs for physically smaller, less obtrusive, and more efficient antennas. As is known to those skilled in the art, there is an inherent paradox between the physical antenna size and the antenna gain, at least with respect to single-element antennas. Increased gain requires a physically larger antenna, while users continue to demand physically smaller antennas. As a further constraint, to simplify the system design and strive for minimum cost, equipment designers and system operators prefer to utilize antennas capable of efficient multi-frequency and wide bandwidth operation. Finally, it is known that the relationship between the antenna frequency and the antenna length (in wavelengths) determines the antenna gain. That is, the antenna gain is constant for all quarter wavelength antennas (i.e., at that frequency where the antenna length is a quarter of a wavelength).
One prior art technique that addresses certain of these antenna requirements is the so-called xe2x80x9cYagi-Udaxe2x80x9d antenna, which has been successfully used for many years in applications such as the reception of television signals and in point-to-point communications. The Yagi-Uda antenna can be designed with high gain (or directivity) and a low voltage-standing-wave ratio (i.e., low losses) throughout a narrow band of contiguous frequencies. It is also possible to operate the Yagi-Uda antenna in more than one frequency band, provided that each band is relatively narrow and that the mean frequency of any one band is not a multiple of the mean frequency of another band.
Specifically, in the Yagi-Uda antenna, there is a single element driven from a source of electromagnetic radio frequency (RF) radiation. That driven element is typically a half-wave dipole antenna. In addition to the half-wave dipole element, the antenna has certain parasitic elements, including a reflector element on one side of the dipole and a plurality of director elements on the other side of the dipole. The director elements are usually disposed in spaced apart relationship in that portion of the antenna pointing in the transmitting direction or, in accordance with the antenna reciprocity theorem, in the receiving direction. The reflector element is disposed on the side of the dipole opposite from the array of director elements. Certain improvements in the Yagi-Udi antenna are set forth in U.S. Pat. No. 2,688,083 (disclosing a Yagi-Uda antenna configuration to achieve coverage of two relatively narrow non-contiguous frequency bands), and U.S. Pat. No. 5,061,944 (disclosing the use of a full or partial cylinder partly enveloping the dipole element).
U.S. Pat. No. 6,025,811 discloses an invention directed to a dipole array antenna having two dipole radiating elements. The first element is a driven dipole of a predetermined length and the second element is an unfed dipole of a different length, but closely spaced from the driven dipole and excited by near-field coupling. This antenna provides improved performance characteristics at higher microwave frequencies.
The present invention discloses an antenna comprising one or more conductive elements, including a horizontal element and one or more vertical elements interconnected by meanderline couplers, and a ground plane. The meanderline has an effective electrical length that affects the electrical length and operating characteristics of the antenna. Further, the antenna conductive elements include one or more radiating wings conductively connected to the horizontal element and substantially parallel to the ground plane. The radiating wings increase the coupling between the ground plane and the horizontal element, improving the antenna gain. Further, the antenna can include one or more tuning wings forming an acute angle with one of the vertical elements to provide a frequency tuning capability for the antenna.